Abstract

We demonstrate and characterize symmetric [3×3] three-dimensional directional couplers fabricated in glass using a high-pulse energy femtosecond laser oscillator. The characteristics of the [3×3] directional couplers closely agree with the theoretical prediction, except for small errors caused by the fabrication process. We show that deviations from symmetry are dominated by vertical position errors of the coupling waveguide.

Coupling characteristics of a fabricat ed [3×3] directional coupler with an optical signal from input port 1. The separations between the coupling waveguides S are designed to be (a) 25 μm, (b) 20 μm, and (c) 15 μm. The solid lines and dotted lines correspond to TM and TE polarization modes, respectively.

Calculated coupling characteristics of [3×3] directional couplers, when (a) the position of waveguide 1 is not aligned correctly, and when (b) the propagation constant of the waveguide is different from the others.